This invention relates to roughing gear shaper cutters used for roughly generating gears, sprockets, splines, cams and like shapes by reciprocation. Roughing cutters are used to remove large amounts of stock quickly from the workpiece until the desired profile is approximated, after which a finishing cutter removes the remaining stock in small amounts to produce the desired profile with a smooth finish. Such a procedure saves time and increases the life of the highly refined and relatively expensive finishing cutter. The profile of the roughly cut shapes is dependent upon the profile of the cutting edges on the roughing cutter. In the past the roughing cutter had a profile designed to leave a substantially uniform amount of stock to be removed in a finishing operation to produce the desired shape. Stuart J. Johnson, in U.S. Pat. No. 3,892,022 issued on July 1, 1975, disclosed that a roughing hob having undulating cutting edges left alternating heavy and light sections of stock to be removed in a finishing operation. During the subsequent finishing operation, chips were more easily broken, reducing the temperature at the cutting edge of the finishing tool and thus increasing the life of the finishing tool and reducing the energy consumed in the operation.
In generating a shape, a hob cuts by rotating about its axis teeth having cutting edges lying in substantially radial planes. In order to provide clearance, the teeth are backed off from the cutting edges in such a manner that, as the hob is repeatedly sharpened, the profiles generated on work pieces by the successively created cutting edges remain constant even though the diameter of the hob is reduced by sharpening.
A gear shaper cutter, in contrast, generates a shape primarily by reciprocation. The cutting is accomplished by radial teeth having cutting edges lying substantially in a plane perpendicular to the axis of the cutter. In order to provide the necessary clearance these teeth are tapered back from the cutting edge at each point along the cutting edge. When the cutter is sharpened, its diameter changes, protuberances in the cutting edge become smaller and recessed in the cutting edge become larger. As a result, the shape generated is altered not only by the change in diameter, but also by the change in the contour of the cutting edge. Johnson's teachings about undulating cutting edges on hobs were, therefore, not applicable to gear shaper cutters, because their contours do not remain constant.